Interpretive Summary: Manure contains both organic and inorganic N. Plants can utilize inorganic N, but organic N must first be converted to inorganic N (mineralized). Estimates of organic N mineralization have been highly variable. The objective of this work was to examine potential manure components (feeds and feed residues, bacterial and colonic cells) to determine factors which may influence the availability of organic N in dairy manure. Mineralization of N and C was studied by incubating samples with soil and monitoring the production of inorganic N and C. Results demonstrated that there was a relationship between C mineralization and the ratio of C to N in the sample when the C/N ratio was less than 15. However, when the C/N ratio was above 15, there was little or no C mineralization. The percent of mineralized ranged from 13% for to 98%; however, inorganic N was converted to organic N (immobilized) in some of the amended soils. There was a strong relationship between the percent of added N that was mineralized and the C/N ratio, and between the amount of N in the amendment and mineralizable N. Manure contains a wide range of compounds that have very rapid or intermediate N mineralization characteristics, or that are very strong immobilizers of N, and these results may help in developing improved estimates of manure N mineralization.

Technical Abstract:
The objectives of this work were to examine C and N mineralization characteristics of potential manure components(feeds and feed residues, urea, bacterial and colonic cells) and to determine factors which may influence the availability of the organic N in dairy manure. Manure N and C mineralizations were determined by incubation of sample-amended soil. Changes in NH4+ and NO3- concentration and the production of CO2 were monitored over 112 d. There was a declining relationship between the initial potential rate of C mineralization and the C/N ratio at C/N ratios less than 15. Above C/N ratios of 15, the initial potential rate of C mineralization was low and non-variable. Mineralized added N ranged from 13% for mature orchardgrass to 98% for urea; however, there was a net N immobilization in the cell wall-amended soils. At C/N ratios less than 40, there was a strong relationship between the percent of added N that was readily mineralized and the C/N ratio. There was also a positive relationship between readily mineralizable N and the N concentration of the amendment. Manure contains a wide range of compounds that have very rapid or intermediate N mineralization characteristics, or that are strong immobilizers of N, and these results may help in developing improved estimates of manure N mineralization.